Thanks to visit codestin.com
Credit goes to www.scribd.com

Scribd
Upload
561 views2 pages

C) 1-Phase Differential Slope Test Procedure: The Relay Testing Handbook

1. The document describes procedures for testing the differential slope settings of transformer relays using a single-phase test method. This involves applying currents to different windings and phases, and calculating ratios to determine compensation factors. 2. Key steps involve applying restraint current to one winding, then increasing current on another until pickup occurs. Calculations are made to determine the infrared ratio, operating point, and expected vs. actual slope settings. 3. Test results for a relay are shown, with currents applied to different windings and phases, and calculations made to analyze pickup performance and percent error compared to specifications.

Uploaded by

sameershahzan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
561 views2 pages

C) 1-Phase Differential Slope Test Procedure: The Relay Testing Handbook

1. The document describes procedures for testing the differential slope settings of transformer relays using a single-phase test method. This involves applying currents to different windings and phases, and calculating ratios to determine compensation factors. 2. Key steps involve applying restraint current to one winding, then increasing current on another until pickup occurs. Calculations are made to determine the infrared ratio, operating point, and expected vs. actual slope settings. 3. Test results for a relay are shown, with currents applied to different windings and phases, and calculations made to analyze pickup performance and percent error compared to specifications.

Uploaded by

sameershahzan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 2

The Relay Testing Handbook

C) 1-Phase Differential Slope Test Procedure


A single-phase test procedure is slightly more complicated because correction factors
may apply. Digital transformer relays use algorithms to compensate for the different
transformer phase shifts as described earlier and apply compensation factors to compare
windings with different configurations. The compensation factors for the example SEL-
387 can be found in the Testing and Troubleshooting section of the instruction manual as
shown in the following table:

WNCTC SETTING A
0 1
Odd: 1, 3, 5, 7, 9, 11 √3
Even: 2, 4, 6, 8, 10, 12 1.5

However, we have found through experimentation that the correction factor is actually 1
WnCTC equals 12 using our test connections.

Follow these steps to test the Differential Slope settings using the Post-Test Calculation
method from the previous “3-Phase Differential Slope Testing” Section:

1. Determine how you will monitor pickup and set the relay accordingly, if required.
(Pickup indication by LED, output contact, front panel display, etc. See previous
publications of The Relay Testing Handbook for details.)

2. Apply a restraint current into the first test phase of Winding-2. The pickup indication
should be on.

3. Apply an equal, but opposite current in W1 using the Tap ratios to determine what the
current magnitude should be. For example:

TAP1 × A1
W1
= W2 ×
TAP2 × A2

2.41 × 1
W1= 5 ×
4.61 × 1.732

W1= 5 × 0.302

W1 = 1.510

4. The pickup indication should now be off. Raise the Winding-1 current until the relay
operates. Record the value on your test sheet. (Remember that you can also use the
pulse or jog method to minimize the amount of current applied to the relay. Review the
Instantaneous Overcurrent (50-element) pickup procedure in previous publications of
The Relay Testing Handbook for details.)

116
Chapter 2: Percent Differential (87) Element Testing

5. Calculate the IRT, IOP, and Slope using the formulas in the Post-Test Calculation section
of the “3-Phase Differential Slope Testing” in this document. Use a 1.732 correction
factor for windings with odd W_CTC settings and use the IRT calculation to determine
if the test was O87P, Slope-1, or Slope-2. Raise the W2 current and repeat 2-5 until all
elements of the differential protection have been tested.

¾
( ) (
IRT=  IAW2 / ( TAP2 × A2 ) + IAW1 / ( TAP1 × A1)  / 2 )
IOP= IAW1/ ( TAP1 × A1)  - IAW2/ ( TAP2 × A2 ) 
¾
¾ EXPECTED=IF(IRT<(O87P × 100 / SLP1),O87P,IF(IRT<3,SLP1,SLP2))

¾ ACTUAL=IF(IRT<(O87P × 100 / SLP1),IOP,IF(IRT<3,100*(IOP/IRT),100*((IOP+1.2)/IRT)))


6. Compare the pickup test result to the manufacturer’s specifications and calculate the
percent error as shown in the following example.

DIFFERENTIAL TEST RESULTS


PICK UP 0.3 TIME DELAY 0 CORR
SLOPE 1 20% TAP1 2.41 W1CTC 12 1
SLOPE 2 60% TAP2 4.61 W2CTC 1 1.732
PICKUP TESTS
TEST IAW2 (A) IAW1 - ICW1 (A) IRT IOP EXPECTED ACTUAL ERROR (%)
1 0.0 A 0.736 0.153 0.305 0.30 0.31 1.80
2 5.0 A 2.239 0.778 0.303 0.30 0.30 0.94
3 15.0 A 5.54 2.089 0.420 20.00 20.11 0.57
4 20.0 A 7.394 2.786 0.563 20.00 20.21 1.06
5 25.0 A 9.923 3.624 0.986 60.00 60.33 0.54
6 30.0 A 12.726 4.519 1.523 60.00 60.26 0.44
TEST IBW2 (A) IBW1 - IAW1 (A) IRT IOP EXPECTED ACTUAL ERROR (%)
7 0.0 A 0.732 0.152 0.304 0.30 0.30 1.24
8 5.0 A 2.24 0.778 0.303 0.30 0.30 1.08
9 15.0 A 5.544 2.090 0.422 20.00 20.19 0.93
10 20.0 A 7.382 2.784 0.558 20.00 20.05 0.26
11 25.0 A 9.902 3.620 0.978 60.00 60.16 0.26
12 30.0 A 12.711 4.516 1.517 60.00 60.17 0.28
TEST ICW2 (A) ICW1 - IBW1(A) IRT IOP EXPECTED ACTUAL ERROR (%)
13 0.0 A 0.732 0.152 0.304 0.30 0.30 1.24
14 6.0 A 2.544 0.904 0.304 0.30 0.30 1.38
15 15.0 A 5.535 2.088 0.418 20.00 20.02 0.12
16 21.0 A 7.753 2.924 0.587 20.00 20.08 0.38
17 24.0 A 9.342 3.441 0.871 60.00 60.17 0.28
18 27.0 A 11.035 3.980 1.197 60.00 60.23 0.38

7. Repeat Steps 2-6 for all three phases.

8. Repeat the pickup test for all windings that are part of the differential scheme. If more
than two windings are used, change all connections and references to W2 to the next
winding under test. (W2 becomes W3 for W1 to W3 tests)

117

You might also like